Vacuum Decay / Pressure Decay Leak Testing

Differential Pressure Decay Leak Test System

Pressure decay is an older technology that has existed for many years. It is an indirect leak flow measurement with a leak rate based on decay rate and test pressure. Test volume is calculated for every set up. It is sometimes called “calibration.” Differential pressure decay offers a higher resolution and cost when compared to pressure decay.

Common Issues with Pressure Decay

Pressure decay gives an indirect measurement when calculating leaks. The changing test volume may give a bias reading. The operator must frequently “calibrate” during a part changeover or the operator can “zero” or mask a leak. Reference volume is required for this method, which is about twice the volume as pressure decay, which means twice the time to fill for each test. A differential pressure transducer is also required. Often, a large (gross) leak will cause an over-range of the differential transducer and damage or destroy it.

The pressure transducer is often not rated for the required resolution and temperature fluctuations can cause errors. For example, an increase in temperature will mask leaks while decreases in temperature will cause false rejects. Both methods are susceptible to these fluctuations and will require frequent “calibration” to overcome drifts. Typically the reference volume must be a “0” leak part. Both systems require extensive maintenance, as well. Consult ATC if you are looking to upgrade or replace your pressure decay or vacuum decay leak test system.

IGLS Micro-Flow vs. Pressure Decay

IGLS Technology

Pressure Decay

Measures direct flow

Measures indirect pressure drop

Is temperature insensitive

Is temperature sensitive

Is volume insensitive

Is volume sensitive

Does not require frequent calibration

Requires frequent calibration (high maintenance)

High accuracy

Lower accuracy

Higher achievable gage R&R

Typically lower or equal instrument cost

Typically 25-35% faster for same capability

Why ATC’s Micro-Flow Test is Faster than Pressure Decay

IGLS Micro-Flow vs. Differential Pressure Decay

IGLS Technology

Diff. Pressure Decay

Measures direct flow

Measures indirect pressure drop

Is temperature insensitive

Is temperature sensitive

Is volume insensitive

Is volume sensitive

Does not require frequent calibration

Requires frequent calibration (high maintenance)

High accuracy

Twice the valves and connections, twice the chance for leaks in the system (high maintenance)

No reference volume required

Reference volume (preferred a “zero leak part”) is required for each test part

Higher achievable gage R&R

Reference volume must be periodically replaced and verified to be a “zero leaker”